Like
planets,
cometsorbit the Sun.
Unlike a planet, the orbit of
a comet is oftenhighlyelliptical and may be very, very long.

A comet can only be seen when it is nearour solar
system,
close to the
Sun.
At other times the comet is
too far away to be seen.

The speed of a cometchanges during its orbit.
As the comet gets closer to the Sun,
the Sun's gravitypulls the comet
towards it and thecomet
gets
faster. Also, the gravitational forces becomestronger as the comet gets
closer to the Sun. The cometis travelling at its fastest when it is closest to the Sun.

As the cometmoves away from
the Sun, the reversehappens.
The Sun's gravitypulls the cometbackwardsand slows it down. The gravitationalforces becomeweaker
as the cometgets further away. The comet istravelling at its slowest when it is furthest from the Sun.